Layer stack configuration in PCB Design - Cell-by-Cell Formula Trace

Concept Flow

[Start] → [Identify layers and thickness] → [Sum thickness values] → [Output total thickness]

This flow shows how the PCB layer stack thickness is calculated by summing the thickness of each layer.

Formula

=SUM(C2:C5)

This formula sums the thickness values in cells C2 through C5 to calculate the total PCB thickness.

Step-by-Step Trace

Step	Operation	Expression	Result	Explanation
1	Reference cells	C2 + C3 + C4 + C5	0.035 + 0.1 + 1.5 + 0.035	Identify thickness values to sum
2	Add first two	0.035 + 0.1	0.135	Sum Top Copper and Prepreg thickness
3	Add Core layer	0.135 + 1.5	1.635	Add Core thickness
4	Add Bottom Copper	1.635 + 0.035	1.67	Add Bottom Copper thickness for total

The total PCB thickness is 1.67 mm after summing all layers.

Variable Tracker

Step	Variable	Value Before	Operation	Value After
1	Sum	0	Add 0.035 (C2)	0.035
2	Sum	0.035	Add 0.1 (C3)	0.135
3	Sum	0.135	Add 1.5 (C4)	1.635
4	Sum	1.635	Add 0.035 (C5)	1.67

Key Moments

Why do we sum cells C2 to C5?

What does the final sum represent?

Why is it important to add each layer's thickness separately?

Sheet Trace Quiz - 3 Questions

Which cells are included in the thickness sum?

A A2 to A5

B C2 to C5

C B2 to B5

D A1 to C1

Key Result

Layer stack configuration sums thickness values of individual PCB layers to find total board thickness.

Transcript

We start by identifying the thickness values in cells C2 to C5. Then, we sum these values step by step: first adding Top Copper and Prepreg thickness, then adding Core thickness, and finally Bottom Copper thickness. The final sum, 1.67 mm, represents the total thickness of the PCB stack.

Practice

1. What is the main purpose of a layer stack configuration in PCB design?

easy

A. To organize the different layers for signal quality and manufacturability

B. To write software code for the PCB

C. To select the color of the PCB

D. To decide the shape of the PCB

Solution

1. Step 1: Understand layer stack role

   The layer stack configuration arranges copper and dielectric layers to ensure proper electrical performance and manufacturability.

2. Step 2: Eliminate unrelated options

   Writing code, choosing color, or shape are unrelated to layer stack configuration.

3. Final Answer:

   To organize the different layers for signal quality and manufacturability -> Option A

4. Quick Check:

   Layer stack = organize layers for function [OK]

Hint: Layer stack = organizing PCB layers for function [OK]

Common Mistakes:

• Confusing layer stack with PCB shape or color
• Thinking layer stack is about software code
• Ignoring the role of layers in signal quality

2. Which of the following is the correct way to describe a layer stack configuration?

easy

A. A list of software functions for PCB control

B. A sequence of copper and dielectric layers with thickness and material specified

C. A set of colors used on the PCB surface

D. A list of drill hole sizes only

Solution

1. Step 1: Identify layer stack components

   Layer stack includes copper and dielectric layers with defined thickness and materials.

2. Step 2: Remove unrelated descriptions

   Software functions, colors, or drill hole sizes alone do not define layer stack configuration.

3. Final Answer:

   A sequence of copper and dielectric layers with thickness and material specified -> Option B

4. Quick Check:

   Layer stack = copper + dielectric layers [OK]

Hint: Layer stack = copper + dielectric layers with thickness [OK]

Common Mistakes:

• Confusing layer stack with software or color settings
• Ignoring thickness and material details
• Thinking drill holes define layer stack

3. Given a layer stack with 4 copper layers and 3 dielectric layers, what is the total number of layers in the stack?

medium

A. 7 layers total

B. 3 layers total

C. 4 layers total

D. 12 layers total

Solution

1. Step 1: Count copper layers

   There are 4 copper layers.

2. Step 2: Count dielectric layers and sum

   There are 3 dielectric layers. Total layers = 4 + 3 = 7.

3. Final Answer:

   7 layers total -> Option A

4. Quick Check:

   4 copper + 3 dielectric = 7 layers [OK]

Hint: Add copper and dielectric layers for total [OK]

Common Mistakes:

• Counting only copper or only dielectric layers
• Multiplying instead of adding layers
• Confusing layers with thickness values

4. A PCB designer wrote this layer stack configuration but the PCB is too thick. Which part is likely causing the issue?

LayerStack = [
  {"type": "copper", "thickness": 0.035},
  {"type": "dielectric", "thickness": 0.5},
  {"type": "copper", "thickness": 0.035},
  {"type": "dielectric", "thickness": 1.5}
]

medium

A. The layer types are incorrect

B. Copper layers are too thick

C. There are too many copper layers

D. Dielectric layer with thickness 1.5 is too thick

Solution

1. Step 1: Review thickness values

   Copper layers have thickness 0.035, which is typical. Dielectric layers have 0.5 and 1.5 thickness.

2. Step 2: Identify unusually thick layer

   Dielectric layer with 1.5 thickness is unusually thick and likely causes overall PCB thickness issue.

3. Final Answer:

   Dielectric layer with thickness 1.5 is too thick -> Option D

4. Quick Check:

   Thick dielectric layer = thickness issue [OK]

Hint: Check dielectric thickness for PCB thickness issues [OK]

Common Mistakes:

• Blaming copper thickness without checking values
• Ignoring dielectric thickness impact
• Assuming layer types are wrong without evidence

5. You need to design a 6-layer PCB with controlled impedance and minimal thickness. Which layer stack configuration approach is best?

hard

A. Use only copper layers without dielectric layers

B. Use thick dielectric layers between all copper layers to reduce cost

C. Alternate thin dielectric and copper layers with precise thickness control

D. Stack all copper layers together and place dielectric layers on top

Solution

1. Step 1: Understand design goals

   Controlled impedance and minimal thickness require precise layer thickness and alternating copper and dielectric layers.

2. Step 2: Evaluate options

   Thick dielectric increases thickness and reduces control. Copper-only or stacking copper layers together ignores dielectric role.

3. Final Answer:

   Alternate thin dielectric and copper layers with precise thickness control -> Option C

4. Quick Check:

   Thin dielectric + copper layers = controlled impedance [OK]

Hint: Alternate thin dielectric and copper for control and thinness [OK]

Common Mistakes:

• Using thick dielectric layers increasing thickness
• Ignoring dielectric layers for impedance control
• Stacking copper layers without dielectric separation